Aqueous jet inks commonly used in ink jet printers are well known. A goal of those who develop aqueous ink jet formulations is to prevent dye-based aqueous ink jet inks from spreading or feathering on a paper substrate and thereby running into one another. Spreading or feathering blurs the edges of a printed type character and can blur or distort a visual image, reducing the possible resolution of the printer. A further goal of the industry is to provide an ink that will be waterfast upon drying on the paper substrate. Several methods have been used in the past to achieve the first objective. For example, materials that act as mordants for the ink have been incorporated into, or coated onto, the paper substrate to prevent feathering. This approach requires that these specially treated and more expensive papers be used to obtain a better definition of the printed characters.
Alternatively, in some previous approaches an extra jet is provided in the print head to deposit such a mordant on the paper in the same spot that the ink is applied, just prior to application of the ink. This method requires incorporation of extra jets in the print head as well as an extra reservoir to contain the mordant. In addition, further electrical circuitry and programming are required to deposit the mordant in the proper place at the proper time. For both of these methods, mordants used are typically cationic in nature since most of the water-soluble dyes that are used are anionic.
For the second objective of providing a waterfast ink, claims have been made that this too is accomplished by the presence of the mordant. However, only unsatisfactory results have resulted in practice. Alternatively, a water-resistant coating may be laminated over the printed substrate. This however, requires an additional step, as well as additional hardware and coating material and has proven to be too expensive for most applications. A third method for achieving a waterfast ink involves the use of pigments rather than dyes. There are several shortcomings to this approach. For one, it is difficult to obtain and maintain pigments in a sufficiently finely divided state in the ink that they do not block the fine orifices (on the order of 25 microns in diameter) of the print heads. In addition, the color range attainable with pigments is more limited than with dyes.
Thus, it would be desirable if an aqueous jet ink could be developed which reduces the feathering of the ink on the substrate while also improving the waterfastness of the ink once it is dry. It would also be desirable to eliminate the need for special and/or additional equipment or the modification of existing jet ink print heads as well as to avoid any extra steps or layers in achieving the waterfastness goals.